These are mainly associated with Gastric Bypass patients but it it good to have a heads up and be aware of any potential deficiencies.

Hyperparathyroidism, due to inadequate absorption of calcium, may occur for some patients (mainly linked to Gastric Bypass (GBP) patients). Calcium is primarily absorbed in the duodenum, which is bypassed by the surgery. Most patients can achieve adequate calcium absorption by supplementation with vitamin D and calcium citrate (carbonate may not be absorbed—it requires an acidic stomach, which is bypassed).

Iron frequently is seriously deficient, particularly in menstruating females, and must be supplemented. Again, it is normally absorbed in the duodenum. Ferrous sulfate can cause considerable GI distress in normal doses; alternatives include ferrous fumarate, or a chelated form of iron. Occasionally, a female patient develops severe anemia, even with supplements, and must be treated with parenteral iron.

Vitamin B12 requires intrinsic factor from the gastric mucosa to be absorbed. In patients with a small gastric pouch, it may not be absorbed, even if supplemented orally, and deficiencies can result in pernicious anemia and neuropathies. Sublingual B12 appears to be adequately absorbed. In some patients, sublingual B12 (cyanocobalamin) does not provide sufficient amounts. In these patients, injections may be needed.

Thiamine deficiency (also known as beriberi) will, rarely, occur as the result of its absorption site in the jejunum being bypassed. This deficiency can also result from inadequate nutritional supplements being taken post operatively.

Protein malnutrition is a real risk. Some patients suffer troublesome vomiting after surgery, until their GI tract adjusts to the changes, and cannot eat adequate amounts even with 6 meals a day. Many patients require protein supplementation during the early phases of rapid weight loss, to prevent excessive loss of muscle mass. Hair loss is also a risk of protein malnutrition.

Vitamin A deficiencies generally occur as a result of the deficiencies that involve the fat-soluble vitamins. This often comes after intestinal bypass procedures such as jejunoileal bypass (no longer performed) or biliopancreatic diversion/duodenal switch procedures. In these procedures, fat absorption is markedly impaired. There is also the possibility of a vitamin A deficiency with use of Xenical or Alli weight loss medications.

Nutritional effects

After surgery, patients feel fullness after ingesting only a small volume of food, followed soon thereafter by a sense of satiety and loss of appetite. Total food intake is markedly reduced. Due to the reduced size of the newly created stomach pouch, and reduced food intake, adequate nutrition demands that the patient follow the surgeon's instructions for food consumption, including the number of meals to be taken daily, adequate protein intake, and the use of vitamin and mineral supplements. Calcium supplements, Iron supplements, protein supplements, multi-vitamins (sometimes pre-natal vitamins are best) and B12 (cyanocobalamin) supplements are all very important to the post-operative bypass patient.

The total food intake and absorbance rate of food will rapidly decline after gastric bypass surgery. After gastric bypass surgery there is an increase in the number of acid producing cells in the lining of the stomach. Many doctors are prescribing acid lowering medications to counteract the high acidity levels. Many patients then experience a condition known as achlorhydia. Achlorhydia is a condition where there is not enough acid in stomach. Patients can develop an overgrowth of bacteria as a result of the low acidity levels in the stomach. A study conducted on 43 post operative patients revealed that almost all of the patients tested positive for a hydrogen breath test, which determined an overgrowth of bacteria in the small intestine. The overgrowth of bacteria will cause the gut ecology to change and will induce nausea and vomiting. Recurring nausea and vomiting will change the absorbance rate of food which contributes to the vitamin and nutrition deficiencies common in post operative gastric bypass patients.

Protein NutritionProteins are essential food substances, contained in foods such as meat, fish and poultry, dairy products, soy, nuts, and eggs. With reduced ability to eat a large volume of food, gastric bypass patients must focus on eating their protein requirements first, and with each meal. In some cases, surgeons may recommend use of a liquid protein supplement. Powdered protein supplements added to smoothies or any food can be an important part of the post-op diet.

Calorie nutritionThe profound weight loss which occurs after bariatric surgery is due to taking in much less energy (calories) than the body needs to use every day. Fat tissue must be burned, to offset the deficit, and weight loss results. Eventually, as the body becomes smaller, its energy requirements are decreased, while the patient simultaneously finds it possible to eat somewhat more food. When the energy consumed is equal to the calories eaten, weight loss will stop. Proximal GBP typically results in loss of 60 to 80% of excess body weight, and very rarely leads to excessive weight loss. The risk of excessive weight loss is slightly greater with Distal GBP.

VitaminsVitamins are normally contained in the foods we eat, as well as any supplements we may choose to take. The amount of food which will be eaten after GBP is severely reduced, and vitamin content is correspondingly reduced. Supplements should therefore be taken, to completely cover minimum daily requirements of all vitamins and minerals. Pre-natal vitamins are sometimes suggested by doctors, as they contain more of certain vitamins than "regular" multi-vitamins. Absorption of most vitamins is not seriously affected after proximal GBP, although vitamin B12 may not be well-absorbed in some persons. Sublingual preparations of B12 will provide adequate absorption. Some studies suggest that GBP patients who took probiotics after surgery were able to absorb and retain higher amounts of B12 than patients who did not take probiotics after surgery. After the distal GBP, fat-soluble vitamins A, D and E may not be well-absorbed, particularly if fat intake is large. Water-dispersed forms of these vitamins may be indicated, on specific physician recommendation. For some patients, sublingual B12 is not enough, and patients may require B12 injections.

MineralsAll versions of the GBP bypass the duodenum, which is the primary site of absorption of both iron and calcium. Iron replacement is essential in menstruating females, and supplementation of iron and calcium is preferable in all patients. Ferrous sulfate is poorly tolerated. Alternative forms of iron (fumarate, gluconate, chelates) are less irritating and probably better absorbed. Calcium carbonate preparations should also be avoided; calcium as citrate or gluconate, 1200 mg as calcium, has greater bioavailability independent of acid in the stomach, and will likely be better absorbed. Chewable calcium supplements that include vitamin K are sometimes recommended by doctors as a good way to get calcium.

Alcohol MetabolismThere was a study that confirmed post operative gastric bypass patients will absorb alcohol at a faster rate than people who have not undergone the surgery. It will also take a post operative patient longer to reach sober levels after consuming alcohol than those who have not undergone the surgery. A study was conducted on 36 post operative patients and a control group of 36 subjects who have not undergone the surgery. Each subject was given a 5 oz of glass of red wine and the alcohol in their breath was measured to evaluate their alcohol metabolism. The gastric bypass group had an average peak alcohol breath level at 0.08%. The control group had an average peak alcohol breath level of 0.05%. It took on average 108 minutes for the gastric bypass patients group to return to an alcohol breath of zero, while it took the control group an average of 72 minutes to return to an alcohol breath of zero[7] . Patients who have undergone gastric bypass surgery will have a lower tolerance than people who have not gone through the surgery. It will also take a gastric bypass patient longer to return to a sober level after drinking alcohol than a person who has consumed alcohol that has not had the surgery.

PicaThere was a study conducted that confirmed the development of pica after gastric bypass surgery due to iron deficiencies. Pica is a compulsive tendency to eat substances other than normal food. Some examples would be people eating paper, clay, plaster, ashes, or ice. A study was conducted on a female post operative gastric bypass patient who was consuming eight to ten 32oz glasses of ice a day. The patient's blood test revealed iron levels of 2.3 mmol/L and hemoglobin level of 5.83 mmol/L. The patient was then given iron supplements that brought her hemoglobin and iron blood levels to a normal level. After one month the patient's eating diminished to two to three glasses per day. After one year of taking iron supplements the patient's iron and hemoglobin levels remained in a normal range and the patient reported that she did not have any further cravings for ice. The patient was eating ice due to the iron deficiencies that occurred after gastric bypass surgery. Low levels of iron and hemoglobin are common in patients who have undergone gastric bypass. Pica is more common in gastric bypass patients who have a history of the condition prior to the surgery